How Old Is Your Cancer?

A patient who receives a diagnosis of pancreatic cancer has only a 5 percent chance of surviving for five years, a harrowing prognosis that scientists have long struggled to understand. Part of the problem, new research suggests, is that the disease is not typically diagnosed until 15 years after the first cancer-causing mutations appear, by which point the cancer has spread and become highly aggressive. The findings indicate that there may be plenty of time for doctors to intervene before pancreatic cancer becomes lethal—an exciting prospect given recent advances in diagnosing the disease early, when it can be successfully removed with surgery and chemotherapy.

In research published recently in Nature (Scientific American is part of Nature Publishing Group), scientists at Johns Hopkins University sequenced the genomes of seven people who had died of late-stage pancreatic cancer. Their tumor cells contained different types of mutations that the scientists traced back in evolutionary time using mathematical models to build a kind of “family mutational tree.” The models suggested that cancer cells appear 10 years after the first cancer-causing mutation arises and that another five years pass before the cancer cells spread and become deadly. The findings question “the pervasive belief that pancreatic cancer is so aggressive and grows so quickly that screening cannot be effectively used,” says study co-author and Johns Hopkins pathologist and oncologist Christine A. Iacobuzio-Donahue.

In the past two years scientists have brought screening techniques for pancreatic cancer closer to reality. In February 2010 researchers at the University of California, Los Angeles, compared RNA found in the saliva of 60 treatable pancreatic cancer patients with the saliva of 30 cancer-free individuals and identified four RNAs that together could correctly identify the cancer 90 percent of the time. And in March 2009 Northwestern University researchers publishing in the journal Disease Markers developed an optical technology that recognizes various stages of pancreatic cancer cells with 95 percent sensitivity. The technique uses light scattering to detect changes in the cells of the duodenum, part of the small intestine adjacent to the pancreas, which can be viewed using minimally invasive endoscopy.

These technologies are not yet available commercially, but early detection using optical tests and blood or saliva analyses should “advance measurably in the next decade,” says David Tuveson, an oncologist at the Cambridge Research Institute in England. Until then, he notes, doctors should consider using current techniques such as CT and MRI scans to screen patients who are at high risk because of family history of the disease. “Recall that our Supreme Court Justice Ruth Bader Ginsburg had a small pancreatic cancer diagnosed in January 2009 when she was undergoing a CT scan,” Tuveson says. One month later doctors removed it successfully and discharged her with a clean bill of health.